问：
.Net Core: Application startup exception: System.IO.FileNotFoundException: The configuration file 'appsettings.json' was not found and is not optional.
答：
问题代码：
public Startup()
{
var builder = new ConfigurationBuilder().AddJsonFile("AppSetting.json");
Configuration = builder.Build();
}
正确代码：
public Startup(IHostingEnvironment environment)
{
var builder = new ConfigurationBuilder().SetBasePath(environment.ContentRootPath).AddJsonFile("AppSetting.json");
Configuration = builder.Build();
}